Ecologists have often proposed that environmental heterogeneity has a positive effect on species diversity. However, the consistency of the relationship and the specific environmental factor responsible for the pattern has frequently been called into question. Topographic heterogeneity is a common factor thought to promote diversity and increase the proportion of endemic species, but has been found to have limited explanatory power. The interaction of topography and climate can create heterogeneous soil moisture conditions across a landscape that affect the distribution of plant species and therefore the diversity of a region. “Effective heterogeneity” describes the outcome of the interaction between topographic or edaphic heterogeneity and local climate. Between regions of similar topographic heterogeneity, differences in precipitation and insolation can create a wide range of soil moisture heterogeneity with the most “effective heterogeneity” for promoting high plant diversity occurring at moderate levels of aridity. This study aims to 1) describe the relationship between topographic heterogeneity, climate, and variability in soil moisture regime, and 2) quantify the contribution of “effective heterogeneity” to plant beta diversity. Topography, soil moisture, and vegetation data were collected at two sites in central Texas in order to begin addressing these questions. The program PARTITION was used to separate the beta component of local plant diversity.

Results/Conclusions

Preliminary results indicate that within a sub-humid climate zone, an increase in topographic heterogeneity results in increased variability of the soil moisture regime both spatially and temporally. As expected, the sub-humid climate results in a wide range of “effective heterogeneity” with regard to soil moisture dynamics. Increased “effective heterogeneity” is positively correlated with plant beta diversity at these sites. This research has the potential to improve our understanding of the local controls on geographic patterns of plant diversity and serves as a framework for predicting the possible effects of climate change on biodiversity.